# [Pw_forum] about the elastic constants computation

Eyvaz Isaev eyvaz_isaev at yahoo.com
Mon Feb 28 08:40:44 CET 2005

Hi,

--- Shaorui Sun <sunsr at ihep.ac.cn> wrote:
>         who could tell me how to identify the
> ealstic constants such as C11,C12 and C44, with
> pwscf?

You can evaluate these constants by means of total
energy calculations. I.e. you have to calculate the
total energy for undistorted and strained (usually,
tetragonal and monoclinic straines) lattices. And then
fitting E(\delta)-E(0) with respect to distorsion by
an appropriate function.

Calculations oh these parameters  via phonons seem to
be less accurate due to the fact that the slope of
acoustic modes in the long-wave limit (i.e. near the
\Gamma point) is very sensitive to parameters used in
such a kind of calculations.

Bests,
Eyvaz.

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